الصيام
Voluntary and obligatory abstention from food and drink from dawn to sunset, described as beneficial for the body alongside its spiritual purpose.
صُومُوا تَصِحُّوا
“Fast, and you will become healthy.” (meaning, not a literal translation)
Worth noting clearly: this specific short phrase is weakly attested despite being extremely widely quoted — but fasting's obligatory and recommended status rests on entirely separate, firmly established Qur'anic and hadith evidence (Surah al-Baqarah 2:183 among others), independent of whether this particular saying is authentic.
Ibn al-Qayyim discusses periodic fasting as giving the digestive organs rest, likening it to how rest benefits any organ subject to continuous work. He frames Ramadan's month-long structure specifically as long enough to produce real physiological benefit while remaining sustainable, distinguishing it from more extreme or prolonged fasting practices he doesn't recommend.
Modern research on intermittent and time-restricted fasting has explored metabolic effects including insulin sensitivity, though findings vary by fasting protocol and individual, and this remains an active area of ongoing research rather than settled clinical consensus.